Die Umfrage des DVGW wurde Anfang 2009 in Zusammenarbeit mit dem Kompetenzzentrum Wasser Berlin gGmbH (KWB) durchgeführt. Der Fragebogen mit insgesamt 16 Fragen (-> Anhang A) zielt darauf ab, einen bundesweiten Überblick zum Brunnenbetrieb und unterschiedlichen Instandhaltungsmaßnahmen derjenigen Wasserversorger zu erhalten, die eigene Brunnen betreiben. Die vorliegende Auswertung wurde am Kompetenzzentrum Wasser Berlin durchgeführt. Nicht enthalten sind die vier ersten Fragen mit den allgemeinen Angaben des beantwortenden Unternehmens und einer Frage zum Thema Energieeffizienz (Seite 1 des Umfragebogens). Diese wurden durch den DVGW selbst ausgewertet (vgl. Plath and Wichmann 2009). Der brunnenbezogene Teil (Seiten 2 und 3) enthielt die vier Themenkomplexe: (1) Stammdaten (Fragen 5 bis 7) Es wurden die absolute Anzahl der in Betrieb befindlichen Brunnen und ihr durchschnittliches Alter erfragt. Diese Fragen dienen der Klassifizierung und Auswertung. Den Brunnenneubau betreffend, wurde eine Angabe zur Budgetplanung erbeten, um die folgenden Fragen zu Brunnenzustand, Alterung und Regenerierung in Bezug zum Neubau setzen zu können. (2) Brunnenbetrieb, Brunnenzustand und Alterung (Fragen 8 bis 11). Zum Brunnenbetrieb wurden die Art der Brunnensteuerung und die während des Betriebes erfassten Daten und Intervalle zur Betriebsüberwachung abgefragt, ebenso die Methoden und Intervalle zur Brunnenzustandsermittlung. (3) Brunnenregenerierung (Fragen 12 bis 14) Die Fragen zur Notwendigkeit, Veranlassung und Erfolgsbemessung von Regenerierungen dienen der Charakterisierung der Instandhaltungsstrategie. (4) Betriebsstrategie (Fragen 15 und 16) Abschließend wurde nach der Betriebsstrategie und einer möglichen Einflussnahme auf die Brunnenalterung durch Änderungen im Betrieb gefragt. Ziel der Auswertung ist es, den Stand der Praxis der Betriebsführung von Brunnen zu erarbeiten. Durch die gekoppelte Auswertung aller vier Themenkomplexe kann weiterhin geprüft werden, inwiefern die festgestellten Betriebs- und Instandhaltungsstrategien von der Größe des Betreibers oder der Altersstruktur der Brunnen abhängen. Durch den Vergleich der erarbeiteten Ergebnisse mit den in DVGW-Arbeitsblatt W125 (DVGW 2004) festgehaltenen Empfehlungen Forschungskann Raum für Verbesserungen, wie z.B. oder Weiterbildungsbedarf identifiziert werden. Gleichzeitig bietet die bundesweite Ermittlung Gelegenheit zur Einordnung des eigenen Standes der Praxis für die einzelnen Betreiber.

The overall project WellMa, which stands for well management, aims at the optimization of the operation and maintenance of drinking water abstraction wells. For this purpose, in addition to a statistical analyses of well data (report D 1.2) and first field investigations to compare various diagnosis methods (report D 1.3), a review of literature during the preparatory phase WellMa1 should answer the following questions: (1) Which processes affecting the well performance and conditions can occur? (2) Which correlation exists between well ageing and well characteristics? (3) How can such well ageing be recognized at an early stage? (4) What is the state of the practice to restore a good performance and condition? (5) What can be done during well design and construction to prevent well ageing? (6) How can well operation be adjusted to slow-down well ageing processes? Based on textbooks, standards and professional articles published in large number since the middle of the nineties, the state of the art was gathered and compared to current practice at BWB and Veolia to identify possibilities for improvement and specify the need for further investigations to be proposed for WellMa2. 1) Three well ageing types involving different processes could be identified. These are chemical, biological and physical clogging. They are closely linked to the characteristics of the exploited aquifer, such as the physical properties of the formation or the chemical composition of the groundwater. 2) The evaluation of these site-specific aquifer characteristics, the impacts from well design and the observed effects on the well performance and condition and their development with time of operation should be used to specify the individual ageing potential for each well site. 3) The early recognition of well ageing implies the need to monitor wells (1) regularly and (2) with comparable methods. As suitable indicators, the development of water levels and discharge rates to calculate the specific drawdown and specific capacity, the pump surveillance and the visible condition of the well interior could be identified. 4) Both, the assessment of the ageing potential and the monitoring of a reference value describing the state of the well lead to the specification of maintenance requirements. Generally, three strategies could be identified, ranging from sheer operation, over reactive maintenance to regular condition assessment and preventive treatment. Concerning the choice of maintenance method, key criteria must always be the well design, its state of construction, the well ageing type and location. Up to now, patterns linking well characteristics and the success of maintenance could not be identified. Thus, maintenance relies on practical experience and the willingness to discuss limitations and disadvantages of methods as open as the advantages on side of the rehabilitation companies. 5) For well design and construction, the technical standards were summarized, describing the necessary steps for proper dimensioning, drilling, choice of materials and final well development. Not only the avoidance of nonconformities and the careful evaluation of the advantages, but also the restrictions of different well design alternatives, e.g. for the accessibility of rehabilitation, assure an optimal well ageing prevention and well operation. 6) Furthermore, well operation could be identified as a key element and critical factor codetermining the lifetime, but at the same time the economic efficiency of a well. It is always a compromise between demand, technical possibilities and economic considerations, for which reason general standards or technical guidance are not available so far. They need to be developed individually considering present well ageing processes and the quantification of impacts. Comparing the state of the art with current practice at BWB and Veolia, room for improvement could primarily be identified for monitoring and subsequent data processing for both, operational parameters (to assess well performance and condition), and maintenance (to evaluate the success of applied treatments). Based on the recommendations derived on this state of the art review, within WellMa2 the effects of measures for preventing and treating well ageing shall be quantified so that the benefits can be assessed for future optimized well management.

The assessment of methods for the diagnosis and distinction of well ageing types and processes with the aim to recommend methods and tools for further fieldwork was part of work package 1 of the preparatory phase WellMa1. Therefore, field tests were carried out at selected well sites with a variety of methods covering standard monitoring methods to assess the constructive state of a well (TV inspections, borehole geophysical methods) and its performance (pump tests) as well as methods aiming at a better process understanding such as the hydrochemical and microbiological analysis of the raw water and clogging deposits. Altogether ten methods were applied at 21 different wells of the Berliner Wasserbetriebe (BWB) covering (i) exposure of object slides during operation and rest periods for microbiological investigations, (ii) BART with test kits for iron-related bacteria (IRB) and slime-forming bacteria (SLYM), (iii) water sampling for the investigation of pristine groundwater organisms, (iv) online measurements of chemical parameters O2, Eh, pH and T and water sampling for chemical analyses (main cations and anions), (v) TV inspections, (vi) three-step pumping tests, (vii) borehole geophysics with Gamma-Gamma-Density scan (GG.D), NeutronNeutron log (NN), Flowmeter (Flow) and Packer-Flowmeter measurement and (ix) Particle countings. The assessment and comparison should originally be completed by a horizontally directed core sampling from different depths from the screen sections of three of the chosen wells. Due to technical difficulties, this was not achieved during this phase of the project. The investigations led to a development and refinement of the methods and approaches. Because of their limited accessibility to the different parts of a well, a combination of methods is always necessary. Especially for the indirect methods like borehole geophysics, an initial assessment of the well condition directly subsequent to construction is essential to provide a basis for the assessment of the well performance development. Generally, the applied standard monitoring methods and diagnosis tools provided the expected identification of a performance deterioration and evidence for the presence of starting materials for clogging processes such as iron, oxygen, iron-related bacteria and particles. Room for improvement could be identified with regard to the reliability, information value and comparability of the tested methods, e.g. by a stepwise combination and extension of the methods to determine the interacting processes from the composition of the deposits. Further investigations should aim at method validation, especially for well monitoring during routine operation (e.g. use of delta h, development of standards for Qs-measurements and TV inspections), and further method development for the ongoing project with scientific investigations to obtain deeper process understanding, e.g. investigating shares of deposits resulting from the different processes (chemical, biological, physical) and relations between the rate of clogging or the location of deposits to well characteristics and site conditions to separate the different well ageing processes. This will then lead to the identification of key parameters that may be influenced to slow down well ageing and keep the well performance and water quality at an optimum.

WELLMA-1, WP 1.2 includes a statistical analysis of Berlin and French well data. The aim is to identify parameters by which the extent of iron related clogging can be assessed and which can be used for grouping the wells for further investigations. The data analysis is based on data on well construction, water chemistry and well operation for about 615 wells in Berlin and 47 in France. The approach is first to do a descriptive analysis of the datasets. It shows amongst others that the French data are not extensive enough to be included in further statistical analysis. They were therefore interpreted individually and added as annex to the report. In the second step, a reliable indicator for iron related clogging in the Berlin wells is identified. This is done by testing the significance of differences in parameters recommended by BWB (Qs, number of H2O2-treatments and results of TV-camera inspections) that indicate either intense clogging or no clogging. The analysis of the reduced dataset reveals that TV-camera inspections are the most reliable cloggingindicator for the Berlin wells for statistical analysis with the current database. Thirdly, the relation of all available constructional, hydro-chemical and operational parameters is checked for four different stages of clogging indicated by the TV-camera inspections. It can be stated that most wells reveal increasing clogging with increasing well age and decreasing depth of the first filter. Clogged wells are characterized often by lower iron and higher manganese and nitrate concentrations, a higher mean total discharge and more operating hours than wells without clogging indication. Finally, the clogging indicator is evaluated by a multiple linear regression. For this, the dependent variable clogging is linked to the ten variables, which are obviously related to clogging processes. Although all comprised parameters are partly related to the clogging intensity of the wells, only well age, depth of the first filter, iron and manganese concentrations as well as operating hours and total discharge have an explanatory value for clogging. However, their total explanatory value of 20% of the variance in clogging is low. Either the most relevant parameters to identify clogging are missing or the selected parameters reveal too much data variability. This can be due to temporal and depth oriented variations what could not be included in the recent analysis. Measurements in mixed raw water cannot characterize all processes involved in iron related clogging. Therefore, several recommendations of well operation and monitoring are given to improve the explanatory power of the data. The most important ones are the development of a more detailed matrix for the evaluation of well condition by TV-camera inspections and an improvement of measurements of specific capacity Qs by constant discharge rates and fully documented initial step pumping tests. Groups of wells that would be useful for more detailed field investigations and further data analysis are: (i) wells with different depth of the first filter, (ii) wells with significant differences in mean discharges (and similar construction and number of switchings), (iii) wells with different amounts of switchings, (iv) wells with similar number of switchings but different filter lengths or pump capacities and (v) wells of different age, but otherwise same construction and operational characteristics.